Amazon announced Thursday the release of a software development kit for its Kindle e-book reader, which will allow developers to build and eventually sell their own applications for the device.

There are only a few hints as to what we'll actually be seeing: Electronic Arts is building some games, smaller game publisher Sonic Boom is creating word games and puzzles, and restaurant review company Zagat is releasing city guides. None of these developer-created apps will be available until later in the year, and the software developer kit is currently in limited beta.

So why's this announcement coming now? Well, it may have something to do with the fact that next Wednesday will see the likely debut of the strongest competitor to the Kindle yet: the shadowy Apple tablet that may be called the iSlate, the iPad, the iGuide, or some name we haven't dreamed up yet.

Apple's device is widely expected to be geared toward the publishing industry, a hub for newspaper, magazine, and book reading in addition to accessing music, games, and video. And with its App Store already a huge success, Apple will enter the market with a major advantage.

Amazon already operates the Kindle Digital Text Platform, a way for authors and publishers to upload and sell their content; earlier this week, perhaps in another move anticipating Apple's entry into the market, Amazon increased the royalties that authors receive from Digital Text Platform sales.